1. Field of the Invention
The present invention relates to an antenna of a mobile communication terminal, and more particularly to a diversity antenna provided inside a mobile communication terminal for preventing the degradation of transmission quality due to fading effects.
2. Description of the Related Art
As mobile communication terminals are miniaturized and decreased in weight, various service functions need to be provided. There is a trend that internal circuits and components adopted in the mobile communication terminals are multi-functioned and also are constantly miniaturized, in order to satisfy the need for the various service functions. Similarly, This trend of the miniaturization and weight reduction are also needed in an antenna, one of the major component of the mobile communication terminals.
Conventionally, a planar inverted F antenna (PIFA) having a low profile structure is employed as an internal antenna configured inside a mobile communication terminal. FIG. 1 is a perspective view illustrating a structure of the conventional PIFA. The conventional PIFA includes a radiating element 2, a shorting pin 4, a coaxial wire 5 and a ground plate 9. The radiating element 2 is fed through the coaxial wire 5, and is connected to the ground plate 9 by the shorting pin 4 so that an impedance match can be achieved. The conventional PIFA must be designed by taking into account the length L of the radiating element 2 and the height H of the antenna according to the width Wp of the shorting pin 4 and the width W of the radiating element 2.
In this PIFA, among beams generated by the induced current to the radiating unit 2, beams directed toward a ground plane are re-induced, thereby reducing the beams directed toward the human body and improving the SAR characteristic. Further, the beams induced toward the radiating unit 2 are increased. This PIFA functions as a square-shaped micro-strip antenna with the length of the radiating unit 2 reduced to half, achieving a low profile structure. Further the PIFA is an internal antenna installed in the mobile communication terminal, thereby being aesthetically designed and protected from external impact.
This PIFA is constantly improved according to a trend of multi-functioning. In particular, a multipath phenomenon can be caused by radio waves reflected from buildings or geographical features in a mobile communication environment. A fading phenomenon in which the amplitude of a received signal varies can be caused by the multipath phenomenon. To reduce this fading phenomenon and achieve desired transmission quality, a diversity antenna consisting of a plurality of antennas is employed.
FIG. 2 is a plane view illustrating the structure of a conventional internal diversity antenna.
Referring to FIG. 2, the conventional internal diversity antenna includes an array of antennas 220 and 221 arranged on a substrate 210. The antennas 220 and 221 are separated from each other. A feeding element (not shown) is formed at one end of each antenna 220 or 221. When power supply voltage is applied to the feeding element, the radio wave of a desired frequency band is radiated through the antenna 220 or 221. However, there is a problem in that a wide space is needed since the above-described conventional antenna array needs a sufficient separation distance between the antennas. Since the antennas 220 and 221 are arranged on the same horizontal plane provided in the conventional diversity antenna and radio waves radiated from the antennas 220 and 221 are directed in the same direction, a mutual complement on a radiation pattern cannot be achieved. Thus, there is a drawback in that the conventional internal diversity antenna cannot provide desired transmission quality.